Linux client questions - Z50S

A couple of questions about Linux clients:

• Is there a write filter?  The SUSE admin guide does not contain the string "filter".  Is the filter off for "admin", on for "thinuser"?  
• If there is no filter, then what protects the flash?
• Can anyone point me to the latest firmware specifically for the Z50S?  All of the images I find on the download page reference the Z50D.  I assume these models do not take an identical image, or else the file naming is unnecessarily misleading.

Thanks.